ASRock Z77 Extreme 4 SLI Bridge

I recently bought a desktop with a Z77 Extreme 4 in it but it did not come with an SLI bridge. I currently have an Nvidia 660 GC 2Gb and plan on getting another but I have no SLI bridge. Does it matter what brand and length I get? I have never SLI'd two card before so I'm new to it.